With respect to metal containers used in food and beverage fields, in consideration of an affect of chemical substance contained in products on human bodies and from a viewpoint of reduction of burden imposed on a global environment in manufacturing steps, a steel sheet used for manufacturing such metal containers has been shifting to a resin coated steel sheet coated with a polyester resin from a painted steel sheet.
In the metal can field, a 2-piece-type can where a can barrel and a bottom rid are integrally formed becomes a mainstream from a conventional 3-piece-type can which is constituted of a can barrel, a top lid and a bottom lid. As a result, a wall thickness of a can barrel portion is reduced thus promoting the saving of resources. A 2-piece can exhibits high degree of working on a side wall thereof compared to a 3-piece can and hence, the 2-piece can requires an excellent adhesive strength between a steel sheet and a coated resin.
As a method of forming a resin-coated 2-piece can, drawing forming, drawing-redrawing forming, stretch drawing forming, stretch ironing forming and drawing-ironing forming are named. In manufacturing a 2-piece can manufactured by using such a resin coated steel sheet, currently, an electrolytic chromium plated steel sheet having excellent adhesion between a base material and a coated resin after working is used. However, in view of the recent flow of placing emphasis on the protection of the environment, there has been a demand for the development of a surface plated steel sheet for a resin-coated steel sheet containing no chromium by not using hexavalent chromium in manufacturing steps of the steel sheet while ensuring excellent adhesion between a steel sheet and a coated resin layer after working.
In food and beverage fields, as a surface treated steel sheet having adhesion without using chromium, a nickel plated steel sheet is used. As a method of enhancing such adhesion, the formation of an uneven shape on a surface of nickel plating has been studied.
As the prior art where a surface of nickel plating of a can-use surface treated steel sheet is formed into an uneven shape, the following methods are known.
For example, patent literature 1 (JP-A-2000-226676) discloses a method where in manufacturing a laminated welding-use steel sheet having excellent weldability, excellent corrosion resistance and excellent film adhesion, tin plating is performed after nickel plating, a nickel-based plating layer and Sn are formed into an alloy by tin melting processing thus enhancing corrosion resistance, and island-like tin is formed thus enhancing adhesion of a film at high temperature.
Patent literature 2 (JP-A-2001-288585) discloses a method where in manufacturing a welded-can-use plated steel sheet which can be welded without removing film particularly, electric tin plating is applied to a steel sheet after forming a nickel diffusion layer, and an SN—Fe—Ni alloy layer is formed by reflow processing, and tin is coagulated by a surface tension of molten steel thus forming island-like tin.
Patent literature 3 (JP-A-2005-256014) discloses a method where nickel-based plating formed of Ni or Fe—Ni alloy plating is applied to a steel sheet to which nitriding processing is applied, Sn plating is performed, and tin melting processing is performed after Sn plating thus forming an Sn—Fe alloy layer or an Sn—Fe—Ni alloy layer containing nitrogen, and island-like tin is formed in an industrially stable manner due to an effect of a nitriding layer.
Further, Patent literature 4 (JP-A-2004-095497) discloses a method where in manufacturing a cathode-can-use steel sheet raw material of an alkali cell, Ni—P plating is applied to the steel sheet raw material, and heat treatment is applied after plating an Ni3P intermetallic compound is dispersed thus forming an extremely fine uneven surface on the steel sheet.